Lithium ion cells with silicon based active materials and negative electrodes with water-based binders having good adhesion and cohesion

Abstract

Polymer binders for negative electrodes with silicon based active materials are described based on poly(acrylamide-co-acrylate salts). Lithium ion batteries incorporating electrodes formed with the binders achieve longer cycling with suitable performance. Mechanical properties associated with each of the moieties of the copolymers are studied to guide polymer selection.

What is claimed is: 
     
       1. A negative electrode for a lithium ion battery comprising:
 an active material comprising a silicon oxide-based active material; 
 nanoscale conductive carbon; and 
 a polymer binder consisting essentially of poly (acrylamide-co-acrylate salt) having at least about 5 mole percent of the acrylate salt moiety and at least about 5 mole percent of the acrylamide moiety 
 wherein the negative electrode on a metal foil current collector has a 180 degree peel adhesion with a force of at least about 6 pound-force/meter and a cohesion corresponding to maintenance of electrode integrity when bent around a mandrel with a diameter of 6 mm. 
 
     
     
       2. The negative electrode of  claim 1  wherein the active material further comprises graphite, and the active material comprises from about 20 wt % to about 100 wt % of the silicon oxide-based material and from about 0 wt % to about 80 wt % of the graphite. 
     
     
       3. The negative electrode of  claim 1  wherein the silicon oxide-based active material comprises a composite comprising carbon, silicon suboxide and optionally nanoscale silicon. 
     
     
       4. The negative electrode of  claim 1  wherein the silicon oxide-based active material comprises silicon suboxide. 
     
     
       5. The negative electrode of  claim 1  wherein the nanoscale conductive carbon comprises carbon nanotubes, carbon black, carbon nanofibers, or mixtures thereof. 
     
     
       6. The negative electrode of  claim 1  wherein the poly (acrylamide-co-acrylate salt) has a sodium, potassium, ammonium or a combination thereof as counter ion. 
     
     
       7. The negative electrode of  claim 1  wherein the poly (acrylamide-co-acrylate salt) has a sodium counter ion and an average molecular weight from about 300,000 g/mole to about 2,000,000 g/mol. 
     
     
       8. The negative electrode of  claim 1  having from about 78 wt % to about 96 wt % of the active material, from about 0.1 wt % to about 7 wt % of the nanoscale conductive carbon; and from about 4 wt % to about 20 wt % of the polymer binder, wherein the poly (acrylamide-co-acrylate salt) comprises poly (acrylamide-co-sodium acrylate). 
     
     
       9. A negative electrode structure comprising a metal foil current collector and the negative electrode of  claim 1  on the current collector and having a 180 degree peel adhesion with a normalized load of at least about 6 lbf/m and a cohesion corresponding to maintenance of electrode integrity when bent around a mandrel with a diameter of 6 mm. 
     
     
       10. The negative electrode structure of  claim 9  wherein the negative electrode has from about 78 wt % to about 96 wt % of the active material, from about 0.1 wt % to about 7 wt % of the nanoscale conductive carbon; and from about 4 wt % to about 20 wt % of the polymer binder, wherein the poly (acrylamide-co-acrylate salt) comprises poly (acrylamide-co-sodium acrylate). 
     
     
       11. A lithium ion cell comprising:
 the negative electrode of  claim 1 ; 
 a positive electrode structure comprising a current collector and on the current collector an electrode comprising a lithium metal oxide, conductive carbon, and a polymer binder; 
 a separator between the negative electrode structure and the positive electrode structure; 
 electrolyte comprising a lithium salt and non-aqueous solvent; and 
 a container enclosing the electrode structures, the separator and the electrolyte. 
 
     
     
       12. The lithium ion cell of  claim 11 
 wherein the lithium ion cell has a capacity at the 700th cycle of at least about 80% of the capacity at the 5th cycle when cycled from the 10th cycle to the 700th cycle between 2.5V and the selected charge voltage at a rate of 1C. 
 
     
     
       13. The lithium ion cell of  claim 11  wherein the negative electrode comprises from about 75 wt % to about 96 wt % of the active material, from about 0.1 wt % to about 7 wt % of the nanoscale conductive carbon and from about 4 wt % to about 20 wt % of the polymer binder. 
     
     
       14. The lithium ion cell of  claim 11  wherein the poly (acrylamide-co-acrylate salt) has a sodium counter ion and an average molecular weight from about 300,000 g/mole to about 2,000,000 g/mol. 
     
     
       15. The lithium ion cell of  claim 11  wherein the silicon oxide-based active material comprises a composite of carbon, silicon suboxide, and optionally nanoscale silicon. 
     
     
       16. The lithium ion cell of  claim 11  wherein the lithium metal oxide comprises lithium cobalt oxide or nickel rich lithium nickel manganese cobalt oxide represented by the formula LiNi x Mn y Co z O 2 , 0.45≤x, 0.05≤y, z≤0.35. 
     
     
       17. The lithium ion cell of  claim 16  wherein the lithium metal oxide further comprises from about 20 wt % to about 80 wt % of (lithium+manganese) rich lithium metal oxide represented by the formula Li 1+b Ni α Mn β Co γ A δ O 2−z F z , where b+α+β+γ+δ≈1, b ranges from about 0.04 to about 0.3, α ranges from 0 to about 0.4, β range from about 0.2 to about 0.65, γ ranges from 0 to about 0.46, δ ranges from about 0 to about 0.15 and z ranges from 0 to 0.2, with the proviso that both α and γ are not 0, and where A is a metal different from lithium, manganese, nickel and cobalt. 
     
     
       18. The lithium ion cell of  claim 11  wherein the lithium metal oxide comprises (lithium+manganese) rich lithium metal oxide represented by the formula Li 1+b Ni α Mn β Co γ A δ O 2−z F z , where b+α+β+γ+δ≈1, b ranges from about 0.04 to about 0.3, α ranges from 0 to about 0.4, β range from about 0.2 to about 0.65, γ ranges from 0 to about 0.46, δ ranges from about 0 to about 0.15 and z ranges from 0 to 0.2, with the proviso that both α and γ are not 0, and where A is a metal different from lithium, manganese, nickel and cobalt. 
     
     
       19. The lithium ion cell of  claim 11  wherein the lithium ion cell has a capacity at the 825th cycle of at least about 80% of the capacity at the 5th cycle when cycled from the 10th cycle to the 825th cycle between 2.5V and the selected charge voltage at a rate of 1C. 
     
     
       20. A negative electrode for a lithium ion battery comprising:
 an active material comprising a silicon oxide-based active material; 
 nanoscale conductive carbon; and 
 a polymer binder consisting of a polymer blend with at least about 75 wt % poly (acrylamide-co-acrylate salt) having at least about 15 mole percent of the acrylate salt moiety and at least about 25 mole percent of the acrylamide moiety, 
 wherein the negative electrode on a metal foil current collector has a 180 degree peel adhesion with a force of at least about 6 pound-force/meter and a cohesion corresponding to maintenance of electrode integrity when bent around a mandrel with a diameter of 6 mm. 
 
     
     
       21. The negative electrode of  claim 20  wherein the polymer blend consists of the up to about 25 wt % polyimide. 
     
     
       22. The negative electrode of  claim 20  wherein the polymer blend consists of the up to about 25 wt % polyacrylate. 
     
     
       23. The negative electrode of  claim 20  wherein the polymer blend consists of the up to about 25 wt % polyacrylamide.